The instrumentation and control systems in operating nuclear power plants typically undergo numerous modifications over the reactor life. Many of the modifications focus on upgrading or replacing the plant instrumentation and control infrastructure. The modifications primarily are driven by the need to resolve emerging safety issues and the need to improve operating efficiencies and thermal power generation.
To offset reductions in baseline operating margins that may accompany the modifications, such modifications often include the requirement to improve instrumentation and process modeling accuracy. Since many existing nuclear power plant control systems are based on a single input/single output architecture, significant simplifications and approximations are made, with concomitant conservatism introduced into the associated protective system setpoints. More particularly, significant conservatism often exists in current single input/single output control systems. These conservatism accommodate system calibration constraints, modeling simplifications, and the constraints of the single input/single output architecture, all of which serve to reduce the desired accuracy and margin between a system setpoint function, which is used to initiate automatic protective functions for the system, and the system operating envelope, which defmes the operating surface of the system. To efficiently accommodate plant modifications that reduce plant operating margins, these conservatism should be eliminated or reduced.
The most direct method of eliminating inherent approximations and assumptions in existing instrumentation and control systems is to modify the instrumentation to accommodate a multiple input/multiple output architecture, usually with the aid of digital microcomputer technology. However, this method is often not pursued in nuclear power plants due to nuclear power plant backfit constraints associated with the modifications. Specifically, it is often not economical to completely replace entire plant instrumentation systems. Typically only the signal processing components are replaced while leaving the original sensor package largely intact.
It would be desirable to improve modeling accuracy for nuclear reactor instrumentation and control systems to take into account parametric dependencies among the system process variables in generating the system setpoint function. It also would be desirable to provide a method for addressing parametric dependencies in plant system modeling, within the constraints of existing control system architectures, for rigorously eliminating control system conservatism to address important third parameter effects in a single input/single output control system.